This invention relates to the field of ultrasonic inspection, and more particularly to apparatus for carrying out such inspection of the underwater portions of a ship hull or other underwater structure for pitting due to corrosion or the like.
Measuring of corrosion pits is not commonly done underwater because there has been no convenient means for doing so. Rather, a diver usually merely estimates the pit depths visually. More precise measurements can be taken using feeler gauges or by replicating the corroded surface with wax or epoxy compounds. These techniques, however, are time consuming and do not provide a read-out above water except by having the diver carry notes or replicas topside.
Considerable advances have been made in assessment of the condition of thickness of underwater hull plates by a diver hand carried ultrasonic transducer probe that is moved along the underwater surface of a hull plate. The return or reflected signals are recorded topside and provide much meaningful data as to hull condition, most notably hull plate thickness. Pitting of the plates, however, is not readily or accurately determined from such data, because the shapes and sizes of pits are such as to provide irregular sonic returns that are difficult, if not impossible, to interpret with confidence as to pit existance and dimensions.